The analysis of atomic spectra, term analysis, has a long
history at Lund University and a worldwide reputation. The
goal of a term analysis is to determine the atomic structure
of a species, i.e. to find the excitation energies of the
various energy levels in an atom or atomic ion relative to
the most bound state, the ground state. The energy difference
between two levels can be measured as the frequency (or wavelength)
of the corresponding transition (spectral line) either in
absorption or emission. The final result is a set of energy
levels, with measured energies and the labels given with a
proper spectroscopic notation.
Fig 1. Part of the Mo II term system, split up in subconfigurations,
4d4(ML)nl, where ML is the parent term.
observed spectral feature may show a small-scale pattern due
to hyperfine structure (hfs) or isotope shift (IS). Both are
effects of the atomic nucleus. Hfs is an internal atomic interaction
between the electrons and the nuclear spin, and IS is a result
of a small difference in the transition wavelength for different
isotopes of an ensemble of atoms.
2. Hyperfine structure in Pr II.
Our term analyses have during the last decades been focused
on neutral, singly and doubly ionized atoms of the transition
elements and rare earth elements.